Dental impressions of prepared and unprepared teeth are a vital step in the fabrication of the prosthetic replacement. Such devices as inlays, onlays, full crowns and bridges as well as removable prosthetic devices require replication with accuracy. By means of an impression or negative duplication of the intraoral site, a dental laboratory can convert this reverse likeness to a positive of the original condition. The materials used for taking the impression have improved and presently the use of elastomers is considered the most accurate, stable and easily handled of the impression materials.
A dental impression tray is usually selected for the particular area of the mouth where the impression is to be taken. To obtain an impression of the teeth and surrounding soft tissue, it is desirable to coat the intraoral site with a low viscosity impression material followed by a separate application of a higher viscosity material. The low viscosity material fills the internal critical surfaces of the oral cavity to provide maximum detail, whereas the higher viscosity material serves as a bulking agent between the low viscosity material and the tray. Additionally, the higher viscosity material serves to develop hydraulic pressure to force the lower viscosity impression material into tight apposition to the oral tissue and hard tooth structure.
A bond is formed between the two impression materials as long as too much time does not elapse between the covering of the teeth with the low viscosity material and the seating of the tray with the higher viscosity material. Otherwise, there will be an imperfect coalescence of the two materials. Moreover, if the higher viscosity material is allowed to begin to set before the tray is seated, it will distort the impression.
Presently, the elastomeric impression materials are blended and premixed by hand from separate containers of catalyst and base with the mixed higher viscosity material added to the tray and separately formed lower viscosity material drawn into a syringe. Not only is the blending of each of the impression materials subject to inconsistency from one operation to another, but the overall operation is both messy and time-consuming, and is, in general, performed in the full view of the patient without regard to asepsis.
The apparatus of the present invention dispenses a plurality of different viscosity elastomeric impression materials from a single source in a predetermined sequence and in a predetermined unit dosage for use in taking a dental impression. In using the apparatus of the present invention there is no mess and the procedure is inherently aseptic.